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According to a meta-analysis of 89 studies published June 7 in a China-themed issue of The Lancet, the number of people with dementia in the world’s most populated country soared from 3.7 million in 1990 to 9.2 million in 2010. The figures eclipse those from the World Alzheimer Report 2012, which estimated 5.4 million dementia cases in China in 2010. Moreover, a report on global disease burden in the special Lancet issue found that the number of deaths in China due to Alzheimer’s disease and other dementias doubled between 1990 and 2010, while mortality rates, especially among women, fell steeply during the same period. With continuing growth of China’s aging population, these findings suggest the nation is heading for a bigger dementia burden than anticipated.

The dementia study was led by senior investigators Wei Wang of Capital Medical University in Beijing, and Harry Campbell and Igor Rudan at the University of Edinburgh Medical School in the U.K. Christopher Murray of the University of Washington in Seattle led the analysis of China health trends with collaborators from China and Australia.

Combing through 12,642 studies published in Chinese or English between 1990-2010 and culling the list to 89 that met inclusion criteria for the meta-analysis, the current effort represents “the most comprehensive epidemiological assessment thus far of dementia and its major subtypes, Alzheimer’s disease and vascular dementia, in mainland China,” noted Chengxuan Qiu of Karolinska Institute, Stockholm, Sweden, in an e-mail to Alzforum. Qiu and colleagues reported last month that dementia risk in Sweden may be waning (see ARF related news story on Qiu et al., 2013), but had no part in the new analysis.

For the current study, researchers led by first author Kit Yee Chan of the University of Melbourne in Australia—where Wang has a joint appointment—analyzed data on a combined 340,247 people from nearly all of China’s 34 provinces. By comparison, the meta-analysis that supported the prevalence estimates in the 2012 World Health Organization (WHO) report on dementia surveyed 25 studies that analyzed 87,761 seniors from just 12 provinces (Dong et al., 2007).

From the more comprehensive analysis, the authors concluded that the number of people with AD increased from 1.9 million in 1990 to 5.7 million in 2010, mirroring the sharp rise in overall dementias. Age-specific prevalence crept up as well. In 1990, the prevalence of AD among people aged 60-64 years was 0.33 percent, whereas by 2010 it had reached 0.55 percent. In the 90-94 age group, AD prevalence climbed from 18.5 to 30.9 percent during that timeframe.

The upsurge of AD cases arises in part from the country’s fast-growing proportion of older adults. On top of that, people are having fewer children, largely due to the one-child policy introduced in 1979. That further intensifies the dementia burden because “young people are less willing to look after their aging parents,” said Wang. Whereas three generations living under one roof used to be the norm, this arrangement is becoming rare, even in rural areas, Wang noted.

As for the increased age-specific prevalence, scientists say this could stem from better diagnostic methods as well as increased public understanding that cognitive impairment may not simply be “normal aging.” Nowadays, “mild cases are more likely to be counted, and severe cases are likely to be more clinically recognized and diagnosed,” wrote Walter Kukull, an epidemiologist at the University of Washington, Seattle, in an e-mail to Alzforum. “With China’s huge population, a small change in an estimated proportion can have dramatic consequences in terms of disease burden (i.e., numbers of cases),” he noted.

Given that China had more AD cases in 2010 than any country in the world, the present study “alone suggests that global estimates of Alzheimer’s disease might need to be revised upwards by at least five million cases, or almost 20 percent,” the authors wrote. In an accompanying editorial, Martin Prince of King’s College London, U.K., agreed that this study has important implications, noting that “any attempt to analyze global data needs to access work published in Chinese.” Of the 89 studies in the current meta-analysis, 80 were written in Chinese.

Beyond greater understanding and improved methods, shifting trends in other diseases could also drive up dementia rates. In the second Lancet study—which used Global Burden of Disease data to measure the impact of more than 200 diseases on mortality and quality of life in China—researchers found huge drops in mortality rates for all age groups between 1990 and 2010. However, the number of deaths due to diabetes, as well as years lost to diabetes-induced disability, each rose over 60 percent during that period. Diabetes and other cardiovascular risk factors such as hypertension and obesity have been shown to correlate with greater dementia risk. This could cause future dementia prevalence in China to be underestimated by up to 19 percent, according to a study cited in Prince’s commentary (see Loef and Walach, 2013).

All told, the data reveal a sobering trend for rising dementia prevalence in China. To address growing needs for long-term care, the Chinese government is amending an old law that restricted care homes to people with no income, no children, and no relatives. Under the revised policy, care homes will be open to all, Prince noted. In addition, cross-sector collaborations and other efforts are afoot to promote evidence-based health policy in China, as outlined in Lancet editorials by Yuanli Liu of the Harvard School of Public Health, Boston, Massachusetts, and Xiaoming Shen of Xinhua Hospital in Shanghai, on the global disease burden analysis.—Esther Landhuis

Comments

The Lancet article by Chan and colleagues is the most comprehensive epidemiological assessment thus far of dementia and its major subtypes (Alzheimer’s disease and vascular dementia) in mainland China. It provides estimates on major measures of epidemiology, for example, prevalence, incidence, and mortality, as well as the disease burden (absolute number of cases) in China. Martin Prince’s comment on this study is excellent.

Dementia is very much an age-dependent disorder; after 65 years of age, both prevalence and incidence rates double every five years. Approximately one in two persons aged 95+ is affected by dementia in a Swedish study (von Strauss et al., 1999), which is confirmed in this study of people in China.

This study showed a slight increase in the age-specific prevalence of dementia from 1990 and 2000 to 2010, which is likely due to methodological issues and increased awareness of dementia by the public and by health professionals. The dramatic increase in the absolute number of patients with dementia over the whole period is likely to be driven by a steadily increasing aging population. Indeed, according to the World Bank, the life expectancy at birth in China was 69 years in 1990, 71 years in 2000, and 73 years in 2010, and the proportion of people age 65+ was 6 percent in 1990, 7 percent in 2000, and 8 percent in 2010.

Over the last few decades and in the future, China faces a rapidly increasing older population, driven primarily by low fertility owing to the long-term one-child policy since the late 1970s and by a substantial increase in life expectancy owing to a decline in late-life mortality as a result of social development and fast economic growth since the 1980s. In recent years, the quick urbanization in China has further accelerated the process of population aging (Gong et al., 2012). In this context, China will face even bigger challenges owing to an older population and dementia than other countries in the world. This is supported by comparing the analysis by Chan et al. to previous studies. For instance, a 2005 Lancet article estimated that the number of people with dementia worldwide would double about every 20 years from 2001 (Ferri et al., 2005), whereas Chan and colleagues’ analysis suggested that the number of patients with dementia in China almost tripled in 20 years from 1990 (3.68 million) to 2010 (9.19 million). In addition, worldwide the number of patients with dementia increased by 46.5 percent, from 24.3 million in 2001 (Ferri et al., 2005) to 35.6 million (Alzheimer Disease International 2010 report), while Chan et al. estimated that in China it increased by 63.5 percent, from 5.62 million in 2000 to 9.19 million in 2010.

To deal with the fundamental challenges of population aging and dementia in China, some key areas need to be further explored: 1) development of a healthcare system covering elderly people living both in urban and rural regions, and 2) development of effective interventions that postpone the onset of dementia and late-life cognitive impairment. The latter is critical to fundamentally reducing the burden of the disease. According to research in Western societies, cardiovascular risk factors (e.g., hypertension, diabetes, obesity) and related disorders (e.g., stroke and coronary heart disease) are important determinants of dementia. Some of these factors and disorders have declined since the 1970s among traditional high-income nations. By contrast, the prevalence of most of these factors and disorders has increased in China, especially with regard to hypertension, diabetes, obesity, and stroke. Intervention strategies targeting these metabolic risk factors are likely to be effective in reducing the risk of dementia or in postponing its onset.

Action items could include national campaigns against chronic, non-communicable diseases that target unhealthy lifestyles and cardio-metabolic risk factors. They would likely reduce the risk of dementia and late-life cognitive impairment as well. Increasing research personnel and boosting the financial investment in research on the health care of elderly people and on specific intervention strategies against dementia would help. In particular, focusing on psychosocial, social-cultural, and vascular risk factors might prove most beneficial.